The present invention relates to a copper sputtering target formed into a pot shape by die forging, and a manufacturing method thereof.
In recent years, the sputtering method for forming a film from materials such as metal or ceramics has been used in numerous fields such as electronics, corrosion resistant materials and ornaments, catalysts, as well as in the manufacture of cutting/grinding materials and abrasion resistant materials.
Although the sputtering method itself is a well-known method in the foregoing fields, recently, particularly in the field of electronics, a sputtering target suitable for forming films of complex shapes and forming circuits is in demand. For instance, a copper target (HCM target) having a pot-shaped, three-dimensional structure is being used.
FIG. 1a illustrates a conventional target, and FIG. 1b illustrates a copper target having a pot-shaped, three-dimensional structure. When using a pot-shaped target, ionization sputtering is employed, and this is characterized in that dense plasma is formed.
A standard planar target is deposited by colliding Ar ions against a target and beating out metal atoms. Contrarily, with ionization sputtering, although the process is the same as a planar target up to colliding Ar ions against a target and beating out metal atoms, the metal atoms are ionized with dense plasma, whereby directivity can be given to the ionized metal atoms. Thus, metal atoms can be filled into deep grooves such as holes.
Generally, a copper target comprising this kind of three-dimensional structure is manufactured by subjecting an ingot or a billet obtained by melting and casting metal to hot forging, annealing, and die forging. Hot forging of the ingot or the billet will destroy the cast structure, diffuse and eliminate air holes and segregation, and, through recrystallization annealing, it is possible to increase the density and strength of the structure to a certain degree.
Subsequently, the material subject to forging and recrystallization annealing is further subject to die forging to obtain a copper target shape of a prescribed three-dimensional structure, recrystallization annealing and stress-relieving annealing are performed after die forging, and surface treatment is ultimately performed to obtain a copper target.
Although this kind of copper target manufacturing method will not cause any problem in the manufacture of a standard planar target, several problems will arise when manufacturing a copper target having the foregoing pot-shaped, three-dimensional structure.
Since there will be locations that will be severely affected and locations that will hardly be affected by the plastic deformation during the die forging to be performed in the manufacture of the target, there are cases where the subsequent structure will differ. For example, locations facing the forging direction will merely be subject to compressive force, while locations along the forging direction; that is, the internal surface of the pot-shaped structure will be subject to strong processing like ironing.
Like this, with locations strongly affected and weakly affected by plastic deformation, the crystal orientation and hardness will differ significantly since the size of the recrystallized grains during annealing before die forging will have a significant influence. In other words, crystals will become refined at locations strongly affected by plastic deformation, and crystals will become coarsened at locations weakly affected by plastic deformation. Further, at the boundary area of such locations strongly affected and weakly affected by plastic deformation, these will be of an irregularly mixed status or gradually changing status in the crystal structure.
In particular, a pot-shaped target requires that the inner face structure is uniform and must have sufficient strength so as to maintain such shape, but this strength could not be obtained conventionally. Thus, as a result of the creep phenomenon, there is a problem in that the flange portion will deform considerably.
Generally speaking, when performing sputtering, finer the target crystals, more uniform the deposition, and it is possible to obtain a film with few generation of arcing and particles, and which is uniform and stable. Therefore, the coarsening of crystal grains and the existences of irregular crystal grains arising during the die forging and subsequent annealing will be problematic in that it will increase the generation of arcing and particles, and deteriorate the quality of the sputter deposition.
Further, a significant variation in the crystalline orientation or difference in the hardness at the respective portions of the target will largely affect the sputter rate, and there is a problem in that the quality of the target will deteriorate.
Accordingly, a copper sputtering target having a pot-shaped structure manufactured by die forging entailed problems of deteriorating the quality of the film resulting from the difference in the hardness of the portions of the target, difference in the crystal orientation, and coarsening and unevenness of crystal grains.